In this study, the mechanical properties of non-crimp fabric (NCF) composite laminates under low-velocity impact and compression after impact (CAI) tests were studied by Scanning electron microscopy (SEM) and Digital image correlation (DIC) techniques. The impact response under different impact times, impact angles, and impact distance is studied. Similarly, in CAI test, DIC technique is used to reveal the whole process of NCF composite compression failure, and SEM is used to reveal the microscopic failure form. The experimental results show that the impact damage process of NCF composites has strong directivity. The concrete manifestation is that the internal failure will extend along the paving direction at the failure layer. The peak load generated under 20 J impact energy is about 1/2 of that under 40 J impact energy. The impact distance is one of the important factors affecting the coupling effect of multiple impacts, and the impact angle has little effect on the internal damage extension. The proportion of internal damage area also supports the relevant view, that is, the average difference in the proportion of internal damage area under different impact distance is about 5%, while the average difference in the proportion of internal damage area under different impact angles is about 3%. During the compression process, the main failure mode is shear failure and the failure mode is brittle fracture. The oblique fracture occurs only when the oblique is 45° and the impact distance is large (50 mm). The impact angle has little effect on the residual compression performance of NCF.

中文翻译：

---

多次冲击损伤和 CAI 能力对 NCF 复合材料的耦合影响

在这项研究中，通过扫描电子显微镜（SEM）和数字图像相关（DIC）技术研究了无卷曲织物（NCF）复合材料层压板在低速冲击和冲击后压缩（CAI）测试下的机械性能。研究了不同冲击时间、冲击角度和冲击距离下的冲击响应。同样，在CAI测试中，采用DIC技术揭示NCF复合材料压缩破坏的全过程，并利用SEM揭示微观破坏形式。实验结果表明NCF复合材料的冲击损伤过程具有较强的方向性。具体表现为，在破坏层内部破坏将沿铺装方向延伸。 20J冲击能量下产生的峰值载荷约为40J冲击能量下的1/2。冲击距离是影响多次冲击耦合效应的重要因素之一，冲击角度对内部损伤扩展影响不大。内部损伤面积比例也支持了相关观点，即不同撞击距离下的内部损伤面积比例平均差异约为5%，而不同撞击角度下的内部损伤面积比例平均差异为约3%。压缩过程中，主要破坏模式为剪切破坏，破坏模式为脆性断裂。仅当斜角为45°且冲击距离较大（50mm）时才会发生斜折断裂。冲击角对NCF的残余压缩性能影响不大。